1. Field of the Invention
The present invention relates to a hydrodynamic bearing type rotary device utilizing a hydrodynamic bearing mechanism and a recording and reproduction apparatus including the same.
2. Background Information
In recent years, hard disc apparatuses using recording discs experience an increase in a memory capacity and an increase in a transfer rate for data. Thus, hydrodynamic bearing type rotary devices suitable for high-speed rotation are used as driving apparatuses for such a type of recording apparatuses.
The hydrodynamic bearing type rotary device mainly formed of, for example, a rotating member to which a recording disc is mounted, a stationary member attached to a housing or the like of the recording apparatus, and a hydrodynamic bearing mechanism for supporting the rotating member so as to be relatively rotatable with respect to the stationary member. Further, the hydrodynamic bearing mechanism is mainly formed of, for example, a tubular sleeve, a shaft positioned on an inner peripheral side of the sleeve so as to be relatively rotatable, a thrust flange fixed to an end of the shaft, a radial bearing portion having a radial dynamic pressure generation groove of a herringbone pattern which is formed on an outer peripheral surface of the shaft, and a thrust bearing portion having a thrust dynamic pressure generating groove of a spiral pattern which is formed on the thrust flange. Between the members of the hydrodynamic bearing mechanism, a lubricating fluid such as oil is filled.
In such a hydrodynamic bearing type rotary device, the rotating member rotates with respect to the stationary member by a rotation driving force generated at a magnetic circuit. As a result, the shaft and the sleeve rotate relatively, and the lubricating fluid flows in the radial bearing portion and the thrust bearing portion. Supporting pressures in a radial direction and an axial direction are produced at both of the bearing portions. This allows the shaft to rotate relatively to the sleeve in a non-contact state, and high-speed rotation of a recording disc can be achieved with a high precision.
However, when there is a bubble in the lubricating fluid, shortage of an oil film may occur in the radial bearing portion and the thrust bearing portion, which may result in deterioration in NPPRO and the like, and a desired bearing property cannot be obtained. Further, the shaft or the sleeve may slide directly on the surface of the other, causing a failure of the hydrodynamic bearing type rotary device.
Thus, a hydrodynamic bearing type rotary device including a hydrodynamic bearing mechanism of a circulation type which discharges bubbles in the lubricating body from the bearing portion by circulating the lubricating fluid (see WO2004/094848 A1). In this hydrodynamic bearing type rotary device, a cover having a circular shape is attached to an end of the sleeve. A fluid reservoir having a circular shape which communicates with the radial bearing portion is formed between the sleeve and the cover. Further, a communication hole which connects a space around the thrust bearing portion and the fluid reservoir is formed in the sleeve. This means that the radial bearing portion, the thrust bearing portion, the communication hole and the fluid reservoir form one communicating space.
In such a hydrodynamic bearing type rotary device, a pumping pressure generated at the radial bearing portion and the thrust bearing portion force the lubricating fluid to flow from the radial bearing portion to the thrust bearing portion, the communication hole, and the fluid reservoir, and to the radial bearing portion again to circulate. Bubbles in the bearing portions flow with the lubricating fluid and are eventually gathered to the fluid reservoir. The gathered bubbles are discharged from a hole provided on the cover. In this way, bubbles in the bearing portion are discharged to the outside one after another in this hydrodynamic bearing type rotary device, and failures caused by bubbles can be prevented.
However, in actual cases, even when the lubricating fluid circulates through the communication hole by a pumping pressure, the bubbles sometime do not flow to the fluid reservoir with the lubricating fluid. For example, even though a circulating mechanism is used, bubbles often remain in a connection portion between the thrust bearing portion and the communicating hole, and do not flow into the fluid reservoir through communicating hole. This means that taking only the circulating force generated by a pumping pressure into account cannot completely solve the problem of poor discharge of the bubbles. The behavior of the bubbles cannot be explained simply by the factors such as dimensions, shapes and the like of the components. It is difficult to predict the behavior of the bubbles based on just the conventional wisdom. Thus, it is desired to elucidate the principle in the behavior of the bubbles and to utilize the principle in designing the hydrodynamic bearing type rotary device in order to realize stable discharge of bubbles.